New Jersey Governor Chris Christie at a news conference in Trenton answering questions about a brewing scandal that public officials orchestrated a massive traffic snarl on the busy George Washington Bridge to settle a political score. (REUTERS/Carlo Allegri)

New Jersey Gov. Chris Christie on Thursday fired a top aide who apparently helped orchestrate massive traffic jams at a busy commuter bridge to settle a score, saying he had been blindsided in the scandal that threatened to tarnish his political image.

Christie also instructed his close adviser Bill Stepien, who served as New Hampshire political director for the Bush-Cheney campaign in 2004, to withdraw from pursuing the state GOP chairmanship and to quit a consultancy for the Republican Governors Association. Christie is leading the powerful governors group in 2014

As Christie apologized publicly for the abrupt lane closings seemingly ordered by some of his staff, which he said he did not know about beforehand, the office of the U.S. Attorney in New Jersey said it was launching an investigation.

Revelations that his staff may have plotted the four-day lane closures at the George Washington Bridge in September, causing hours-long jams that stalled commuters, school buses and ambulances, come as Christie has emerged as a powerful figure in the Republican Party and a possible presidential contender.

The controversy erupted with the release on Wednesday of incriminating emails showing Christie's aide and allies appearing to plan lane closings to punish the Democratic mayor of Fort Lee, at the New Jersey end of the bridge, because he had declined to endorse Christie's reelection effort.

"I am embarrassed and humiliated by the conduct of some of the people on my team," Christie said. "I am who I am, but I am not a bully."

As the head of the party's governors association and a possible 2016 White House contender, the tough-talking governor has sought to present himself as a leader who can work with opponents and forge bipartisan alliances.

A former Christie aide adviser implicated in the email scandal, Stepien, spent a lot of time in the Granite State a decade ago, serving as New Hampshire political director for the Bush-Cheney campaign in 2004. Stepien also was John McCain's national field director in 2008.

Steve Duprey, a Republican National committeman from Concord, said he doesn't think the email scandal will hurt Christie should he run for President in two years.

"In the long run, I think it's much ado about nothing," said Duprey, who is neutral because of his RNC post.

"If Gov. Christie were to campaign in New Hampshire, I don't think the average New Hampshire person gives a ... darn about a staff aide illegally or inappropriately closing exit ramps in New Jersey.

"Beyond that, this may actually benefit Gov. Christie in the long run because he showed something that is both refreshing and in very short supply in Washington, which is the ability to take responsibility, to own up to a mistake, acknowledge he's in charge of the team even when people did things wrong that he didn't know about, apologize and correct course," said Duprey, a former state party chairman.

Duprey, a top McCain aide, said he didn't know Stepien well.

Matt Mowers, the executive director of the New Hampshire State Republican Committee, previously served as regional political director for Christie's gubernatorial campaign last year. From 2010-2013, Mowers was regional director for legislative and intergovernmental affairs in the N.J. Governor's Office with Christie.

Christie said at his news conference that he dismissed his deputy chief of staff, Bridget Anne Kelly, who in the most damning email, wrote to a Port Authority executive in August, saying: "Time for some traffic problems in Fort Lee."

The executive, David Wildstein, replied: "Got it."

Wildstein later admitted ordering the lane closures and resigned his post.

The emails were supplied to the media by Wildstein in response to a subpoena issued by a panel of state lawmakers.

He appeared before the panel on Thursday but declined to answer questions, repeatedly invoking the constitutional protection not to say anything that might incriminate him.